This invention relates to an apparatus and a method for reducing in size a medical device such as a stent, stent-graft, graft, or vena cava filter. The apparatus may be used in particular for fastening a medical device onto a catheter.
Medical devices such as stents, stent-grafts, grafts, or vena cava filters and catheters for their delivery are utilized in a number of medical procedures and situations, and as such their structure and function are well known.
A stent, for example, is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Stents are typically inflation expandable or self-expanding. Self expanding stents which are constrained by a sheath or other restraining means, must be provided in a reduced diameter.
An example of a stent described in PCT Application No. 960 3092 A1, published Feb. 8, 1996.
In advancing a stent through a body vessel to the deployment site, the stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. Stents that are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location. The stent must be crimped in such a way as to minimize or prevent altogether distortion of the stent and to thereby prevent abrasion and/or reduce trauma of the vessel walls.
In the past, this crimping or size reduction has been done by hand often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped or otherwise reduced in size multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon.
Recently, stent crimping devices have been disclosed in U.S. Pat. No. 5,546,646 to Williams et al, U.S. Pat. No. 5,183,085 to Timmermans et al., U.S. Pat. No. 5,626,604 to Cottone, Jr., U.S. Pat. Nos. 5,725,519, 5,810,873 to Morales, WO 97/20593 and WO 98/19633.
A cam actuated stent crimper, shown in FIG. 1, employs a plurality of arc-shaped or curved slots with semi-circular ends, disposed such that each slot or cam engages a cam follower bearing 22. The arc-shaped or curved surfaces of the slots are inclined to be non-concentric relative to the axis of rotation 26, and therefore rotation of the cam plate 28 transmits equal radial displacements to the cam follower bearings 22, to simultaneously actuate a like number of linear bearings 24, which have their corresponding linear tracks or rails mounted on a fixed plate. As shown in FIG. 1 the cam plate rotary drive 29 comprises a pneumatic cylinder mounted on a pivot or trunnion, arranged with the cylinder rod connected rotatably to a short arm fixed rigidly to the cam plate. Accordingly, linear motion produced by the pneumatic cylinder translates into controllable arcs of motion of the circular cam plate, which has a projecting V-shaped profile on its outer edge in rolling engagement with three equally spaced rollers with mating inverse V-shaped profiles to provide precise rotatable support to the cam plate. Depending on the direction of rotation, the linear slides which each carry a radially disposed crimping blade, are either moved inwards to apply a crimping force to the stent, or outwards to release the stent. Also when crimping, depending on the degree of rotation of the cam plate, a specific radial crimping displacement may be obtained to match the diametral reduction required for any particular stent.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
It would be desirable to produce a device capable of crimping a stent uniformly while minimizing the distortion of and scoring and marking of the stent due to the crimping. The present invention is directed to that end.
The present invention is particularly concerned with the crimping and otherwise reducing in size of inflation expandable stents, self-expanding stents and other expandable medical devices. For the purpose of this disclosure, it is understood that the term xe2x80x98stenxe2x80x99 includes stents, stent-grafts, grafts and vena cava filters. It is also understood that the term xe2x80x98crimpingxe2x80x99 refers to a reduction in size or profile of a stent.
In the description that follows it is understood that the invention contemplates crimping a medical device either directly to a catheter tube or to a catheter balloon which is disposed about a catheter tube. When reference is made to crimping a medical device to a catheter, a balloon may be situated between the medical device and the catheter tube or the medical device may be crimped to a region of a catheter tube directly. The invention also contemplates crimping a stent in the absence of a catheter to reduce the stent in size.
The present invention is directed, in one embodiment, to an apparatus for reducing a medical device in size. Desirably, the medical device is a stent, a stent-graft, a graft or a vena cava filter, whether self-expandable, balloon expandable or otherwise expandable, although the inventive apparatus may also be employed with any other suitable, generally tubular medical device which must be reduced in size.
The inventive apparatus comprises at least three coupled movable blades disposed about a reference circle to form an aperture whose size may be varied. Each blade is in communication with an actuation device which is capable of moving the blade to alter the size of the aperture. Each blade includes a single radial point on the surface of the blade which a) lies on the circumference of the reference circle prior to movement of the blade, and b) may be moved only along a radius of the reference circle on movement of the blade.
The apparatus further includes an actuation device which comprises a cam and a plurality of linear slide devices. Each linear slide device is in communication with a blade. Each of the linear slide devices is also in mechanical communication with the cam. Rotation of the cam results in linear translation of the slide device and blade, such that the slide device moves along an axis parallel to the radius on which the radial point of the blade lies or along the radius itself.
The invention is also directed to an apparatus similar to that described above, with blades disposed about a reference tube to form a tubular aperture whose size may be varied. Each blade is in communication with an actuation device which is capable of moving the blade to alter the size of the tubular aperture. Each blade includes a single line which a) lies on the surface of the reference tube prior to movement of the blade, and b) may be moved only along a radial plane of the reference tube on movement of the blade.
The inventive apparatus finds particular utility in crimping a medical device such as those mentioned above to a catheter or to a balloon disposed about a catheter.
The inventive apparatus also finds utility in reducing the diameter of a medical device such as those mentioned above prior to crimping.
The invention is also directed to a method of manipulating a medical device which comprises the steps of providing the medical device and providing at least three blades capable of applying a radial inward force. The blades are disposed about a reference circle to form a shrinkable aperture. A medical device such as a stent is placed into the shrinkable aperture and the blades simultaneously moved inward to apply a radial inward force to the medical device. The blades are constructed and arranged such that each blade has a single point which a) lies on the circumference of the reference circle prior to movement of the blade, and b) is moved along a radius of the reference circle on movement of the blade.
The inventive apparatus may also be used as a variable size balloon mold. To that end, the invention is further directed to a method of molding a medical balloon. In the practice of the method, a balloon preform prepared through any suitable technique known in the art is provided. The preform is placed in an apparatus which has a shrinkable tubular aperture formed by at least three movable blades disposed about a reference tube. The blades are constructed and arranged such that each blade has a single line which a) lies on the surface of the reference tube prior to movement of the blade, and b) is moved along a radial plane of the reference tube on movement of the blade. The aperture may be set to a predetermined size prior to placement of the preform therein or after placement of the preform therein. An inflation fluid is supplied to the balloon preform to expand the balloon preform until it contacts the blades. The preform may optionally be heated prior to, during or after the blowing step. The thus formed balloon is then pressure relieved and removed from the apparatus.